The present invention relates to valve assemblies for controlling fluid flow. It finds particular application in controlling a flow of exhaust gases through the intake manifold of an automotive engine to improve cold running performance. It is to be appreciated, however, that the invention has other applications in both automotive and non-automotive areas, such as controlling air recirculation in air conditioners and heaters, ventilation air, and the like.
Heretofore, pneumatically operated flow control valves have been used to control exhaust gas flow through cross-over passages of automotive engines intake manifolds. The prior art cross-over passage control valves were inserted into a circular bore which intersected the cross-over passage. The cross-over valves included a powdered metal or sintered mounting base to which a generally cylindrical or cup-like cage was brazed. The cup-like cage had a pair of large apertures in opposite side walls to allow the exhaust gases to flow in one and out the other. A butterfly plate mounted on a rotatable shaft was positioned within the cage. The inner cylindrical surface of the cage was machined larger in diameter in diametrically opposed quadrants to permit the butterfly plate to be rotated over a 90.degree. arc. By rotating the butterfly plate parallel to the exhaust gas flow, exhaust gases were free to pass through the valve substantially unobstructed. Rotating the butterfly plate transverse to the exhaust gas flow sealed it against the edges of the machined quadrants and blocked the flow of exhaust gases. The butterfly shaft extended through the mounting base in which a TEFLON lip seal blocked exhaust gases from escaping between the base and the butterfly shaft. The butterfly shaft was connected with a lever arm which in turn was connected with a pneumatic actuator that selectively rotated the butterfly plate.
One of the problems with the prior art control valves resides in the difficulty encountered in brazing the cage to the powered metal mounting base. Powered metal parts tend to absorb the braze material.
Another problem with the prior art control valve resides in the corrosion potential of the braze alloy. Under the elevated temperature of exhaust gases, the braze alloy oxidizes causing scaling and fluxing. Oxides of carbon, nitrogen, sulfur, and phosphorous in the exhaust gases tend to react with the brazed metal. Further, chlorides in the exhaust gases can form fluxing salts which fuse at high temperatures. Although high temperature corrosion problems may be overcome using noble metal brazes, such as gold filler, such brazes are unduly expensive.
Another problem arises in the prior art control valve brazes from moisture in the exhaust gases. First, moisture in the exhaust gases contains hydrochloric, sulfuric, and nitric acids. Second, the condensed moisture causes disimilar metal attack at the braze line. This can lead to complete braze separation and stress corrosion cracking at the brazed joint.
Other problems with brazed joints includes brittleness, poor thermal expansion matching with the parent metal, difficulty in nondestructive inspection and quality control, brazing furnace safety, and the cost of brazing furnace maintenance and operation.
The present invention contemplates a new and improved manifold cross-over control valve which overcomes the above referenced problems and others.